PHP installation failed?

I just followed the LAMP stack tutorial and added a very simple test page to /usr/share/htdocs to be sure that php is working.

It's not working. I get a "Forbidden" page, saying I don't have permission to access the file.

I'm very new to setting up apache and php, so I have very little idea of where to start looking for the problem. I'm pretty sure I followed the tutorial exactly as it said to do it. What might I have missed?